Photoreactive suturing of biological materials

ABSTRACT

Materials and methods for photoreactive suturing of biological tissue are disclosed. The suture material includes a structure adapted for positioning at an anastomotic site and has at least a portion of the structure formed by a photoreactive crosslinking agent, such that upon irradiation of the structure the crosslinking agent adheres to the biological material. In one embodiment, the suture material can also include a high tensile strength element which is coated with a laser activatable crosslinking agent or glue. The suture methods can be practiced manually, or with various apparatus, such as endoscopes, catheters or hand-held instruments.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 538,977 filed Jun. 15, 1990, now U.S. Pat. No. 5,071,417.

BACKGROUND OF THE INVENTION

The technical field of this invention is surgery and, in particular,method and materials for joining living tissues and promoting thehealing of small biological structures.

The conventional approach to joining tissue segments following surgery,injury or the like, has been to employ mechanical sutures or staples.While these techniques are often successful, there are a number oflimitations inherent in such mechanical approaches. First, the practiceof suturing or stapling tissue segments together is limited by theeyesight and the dexterity of the surgeon which can present a severeconstraint when anastomosing tiny biological structures. Second, whendelicate biological tissues or organs are sutured, even minimal scarringcan affect the function of the structure. Finally, suturing can be lessthan satisfactory, even when properly performed, because of the gapswhich are left between the stitches, the inherent weakness of the joint,or the possibility of progressive structural weakening over time.

Various researchers have proposed the use of laser energy to fusebiological tissues together. For example, Yahr et al. in an article inSurgical Forum, pp. 224-226 (1964), described an attempt at laseranastomosis of small arterial segments with a neodymium laser. However,the neodymium laser used by Yahr et al. operated at a wavelength ofabout 1.06 micrometers was not efficiently absorbed by the tissue,requiring large amounts of energy to effect fusion, while also affectingtoo large of a tissue volume.

Further research on laser fusion involving various alternative lasersources, such as the carbon dioxide laser emitting laser light at about10.6 micrometers, the argon laser emitting light at about 0.50micrometers, and the ruby laser emitting light at about 0.70micrometers, continued to encounter problems. In particular, the outputof carbon dioxide lasers was found to be heavily absorbed by water andtypically penetrated into water-laden tissue only to a depth to about 20micrometers. This penetration depth and the resulting bond induced bycarbon dioxide laser fusion was too shallow to provide durable bondingin a physiological environment.

Argon and other visible light laser also produced less than satisfactoryeffects. The output of argon lasers and the like was found to be heavilyabsorbed by blood and subject to substantial scattering within thetissue. These effects combined to create a narrow therapeutic "window"between a proper amount of energy necessary for laser fusion and thatwhich induces tissue carbonization, particularly in pigmented tissuesand tissues that have a high degree of vascularization. Moreover, argonlasers have been particularly cumbersome devices, requiring largeamounts of electricity and cooling water.

Recently, the development of new solid state laser sources have madeprospects brighter for efficient, compact laser fusion systems suitablefor clinical use. Such systems typically employ rare earth-doped yttriumaluminum garnet (YAG) or yttrium lithium fluoride (YLF) oryttrium-scadium-golilinium-garnet (YSGG) lasers. See, for example, U.S.Pat. Nos. 4,672,969 and 4,854,320 issued to Dew, disclosing the use of aneodymium-doped YAG laser to induce laser fusion of biological materialsand to obtain deeper tissue penetration. However, even with such solidstate laser sources, the problems of scattering and damage to adjacenttissue remain. The Dew patents disclose the use of computer look-uptables to control the laser dose based on empirical data.

The absorptive properties of biological structures differ considerablyfrom one tissue type to another, as well as from individual toindividual, making dosage look-up tables often unreliable. There existsa need for better methods and materials for accurately controlling theformation of anastomotic bonds which avoid thermal damage and achieveoptimal results. In particular, non-mechanical suture materials whichcan take advantage of laser or other high energy light sources to joinbiological materials together or otherwise make repairs to delicate bodytissues would satisfy a long-felt need in the art.

SUMMARY OF THE INVENTION

Materials and methods for photoreactive suturing of biological tissueare disclosed. The suture material includes a structure adapted forpositioning at an anastomotic site and has at least a portion of thestructure formed by a photoreactive crosslinking agent, such that uponirradiation of the structure the crosslinking agent adheres to thebiological material. In one embodiment, the suture material can alsoinclude a high tensile strength element which is coated with a laseractivatable crosslinking agent or glue. The suture methods can bepracticed manually, or with various apparatus, such as endoscopes,catheters or hand-held instruments.

The present invention can employ various "biological glue" materials ascrosslinking agents in either solid, liquid, gel or powder form to forma bond to tissue segments and thereby hold them together while naturalhealing processes occur. The crosslinking agents should be biocompatibleand are preferably biodegradable over time in vivo. Examples of suchcrosslinking agents include collagen, elastin, fibrin, albumin andvarious other photoreactive polymeric materials.

Various strength enhancing agents can also be incorporated into thesuture structure to provide additional tensile support along and acrossthe anastomosis. Such high tensile strength elements can be formed frompre-crosslinked segments of the same material that forms thephotoreactive crosslinking agent, or they can be formed from strips orfibers of other natural or synthetic biodegradable materials such ascotton or polyesters, to enhance the strength of the bond.

The present invention permits the creation of anastomoses of biologicalstructures with the optimal use of appropriate laser energy, minimizingthe total energy delivered to the site while obtaining maximum bondstrength and integrity. The terms "anastomosis" and "anastomotic site"are used herein to broadly encompass the joinder of biologicalstructures, including, for example, incision and wound healing, repairof blood vessels and other tubular structures, sealing of fissures,nerve repairs, reconstructive procedures, and the like.

The present invention is preferably practiced in conjunction with a highenergy light source, such as laser, for delivery of a beam of radiationto an anastomotic site, and can also employ a reflectance sensor formeasuring light reflected from the site and a controller for monitoringchanges in the reflectance of the light from the site and controllingthe laser in response to the reflectance changes.

In one embodiment, the laser radiation is delivered through a hand-heldinstrument via an optical fiber. The instrument can also include one ormore additional fibers for the delivery of illumination light orradiation from a laser diode (which can be broadband or white light orradiation from a laser diode) which is reflected and monitored by thereflectance sensor. Reflectance changes during the course of thesuturing operation at one or more wavelengths can be monitored (orcompared) to provide an indication of the degree of tissue crosslinkingand determine when an optimal state of fusion has occurred.

In the present invention, reflective feedback is used to monitor thestate of crosslinking of the suture material with the biologicalmaterial, as well as the degree of fusion or coagulation of thebiological structures so as to allow an optimal dose by eithermanipulation of the energy level or exposure time, or by controlling thesweep of energy across an exposure path. Reflectance changes can also beemployed by a control means in the present invention to adjust orterminate laser operation.

Various light sources can be employed, including gas, liquid and solidstate laser media. Because the present invention permits the user tocarefully monitor the energy dosage, solid state lasers can be utilizedinstead of the more conventional (and cumbersome) gas lasers. Such solidstate laser include optically-pumped (e.g., lamp or diode pumped) lasercrystals, diode lasers, and diode pumped optical fibers. Tunable lasersources can also be used to practical advantage in the presentinvention. In some applications, high intensity flash lamps can also beemployed in lieu of a laser source. Since the feedback control systemsdisclosed herein eliminate (or reduce) the need for look-up tables, atunable laser source can be used to full advantage by matching the laseroutput wavelength with the absorptive and/or dimensional characteristicsof the biological structures to be repaired or otherwise joined. In oneembodiment of the invention, the laser source can be tuned over at leasta portion of a wavelength range from about 1.4 micrometers to about 2.5micrometers to match particular tissue profiles.

In another aspect of the invention, a real-time display means isdisclosed which can be incorporated into a surgical microscope orgoggles worn by the clinician during the procedure to provide a visualdisplay of the state of tissue coagulation simultaneously with theviewing of the surgical site. The display can reveal reflectance valuesat one or more specific wavelengths (preferably, chosen for theirsensitivity to the onset and optimal state of tissue crosslinking), aswell as display a warning of the onset of tissue carbonization.

In one method, according to the invention, a technique for photoreactivesuturing of biological structures is disclosed in which laser energy isapplied to join together two or more tissue segments via a suturestructure that includes a photoreactive crosslinking agent, while thereflectance of light from the irradiated site is monitored. Changes inscattering due to crosslinking of the tissue and crosslinking agent willcause reflectance changes. The reflectance can be monitored in real-timeto determine the optimal exposure duration or aid as visual feedback inthe timing used in sweeping the energy across the anastomosis during thesuturing procedure.

The method can further be enhanced by employing a suturing materialwhich incorporates high tensile strength elements, and/or by coating theentire anastomotic site with a biological glue. The reinforcing stripsprovide load support across and along the repair line, and preferablyare also bonded by the crosslinking agent to the tissue, itself,providing superior bond strength.

The depth of penetration of the laser energy can be controlled in oneembodiment by tuning a mid-infrared laser along a range of wavelengthsfrom about 1.4 micrometers to about 2.5 micrometers to adjust thepenetration to match the desired weld depth. Tuning can be accomplished,for example, by mechanical or electro-optical variation in theorientation of a birefringent crystal disposed in the laser beam path.

This allows the clinician to select a weld depth appropriate to the sizeand type of structures to be welded. This feature of the invention canbe particularly advantageous with delicate biological structures whereaccuracy is needed to crosslink only what is necessary for temporarystrength, while avoiding thermal denaturing of critical structures thatcannot function once scarred. In most instances, the patient's body willmetabolize the suture material over time simultaneous with (orfollowing) the natural healing of the repair site by physiologicalprocesses.

The invention will next be described in connection with certainillustrated embodiments; however, it should be clear by those skilled inthe art that various modifications, additions and subtractions can bemade without departing from the spirit or scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a photoreactive suturing systemaccording to the present invention;

FIG. 2 is a perspective view of a clinical system embodying theprinciples of the invention;

FIG. 3 is a schematic illustration of a suture material incorporating ahigh tensile strength element according to the invention;

FIG. 4 is a schematic illustration of another suture material accordingto the invention;

FIG. 5 is a schematic illustration of a yet another suture materialaccording to the invention;

FIG. 6 is a schematic illustration of a further suture materialaccording to the invention;

FIG. 7 is a schematic illustration of a suture material and detachablecarrier according to the invention;

FIG. 8 is a schematic illustration of a tubular suture materialaccording to the invention;

FIG. 9 is a schematic illustration of a staple-like suture materialaccording to the invention;

FIG. 10 is a more detailed schematic diagram of a laser source useful inthe system of FIG. 1;

FIG. 11 is a partial, cross-sectional view of a laser beam deliveryhandpiece according to the invention;

FIG. 12 is a front view of the laser delivery handpiece of FIG. 11;

FIG. 13 is front view of a surgical instrument incorporating both asuture means and a laser means according to the invention;

FIG. 14 is a more detailed schematic diagram of reflectance monitor foruse in the present invention; and

FIG. 15 is a schematic illustration of a clinical eyepiece view showinga "heads-up" display of reflectance measurements according to theinvention.

DETAILED DESCRIPTION

In FIG. 1, a schematic block diagram of a photoreactive suturing system10 is shown, including a laser 12, power supply 14, controller 16 andphotoreactive suturing material 36. The system can further include abeamshaping/delivery assembly 20, illumination source 22, reflectancemonitor 18, display 24 and tuner 26. In use, the output of laser 12 isdelivered, preferably via beamshaping/delivery assembly 20, to ananastomotic site 30 to fuse the suture material 36 on opposite sides ofa fissure or cleavage line 32 in a biological material. As the laserbeam irradiates exposure zone 34, a crosslinking reaction occurs to fusethe suture material and the biological tissue in the vicinity of thesite 30. The degree of crosslinking can be determined by the reflectancemonitor 18, which provides electrical signals to controller 16 in orderto control the procedure. The reflectance monitor 18 preferably receiveslight reflected by the site from a broadband or white light illuminationsource 22. In addition to controlling the laser operation automatically,the reflectance monitor 18 and/or controller 16 can also provide signalsto a display 24 to provide visual (and/or audio) feedback to theclinical user, thereby permitting manual control. Tuner 26 can also beemployed by the user (or automatically controlled by controller 16) toadjust the wavelength of the annealing radiation beam.

FIG. 2 provides further schematic illustration of the photoreactivesuture system 10 in use. The electrical and optical components of thesystem can be housed in a system cabinet 60 suitable for use in anoperating room or other clinical environment. The laser output isdelivered to the patient by an optical fiber cable 62 (which can includemultiple optical fibers as detailed below) and a handpiece 64. Thesystem is preferably used in conjunction with a surgical microscope (orgoggles) 66 which are adapted to provide a "heads-up" display to theuser. Display signals from the system cabinet 60 are transmitted to themicroscope (or goggles) 66 by cable 68. The laser output can also bedelivered to a remote site via an arthroscope, endoscope or catheter andthe display features of such an instrument can be similarly adapted toprovide the user with data on progress of the crosslinking reaction.

The suture materials of the present invention can take various forms. Inthe simplest embodiment, the suture material comprises a strip or strandof a photoreactive crosslinking agent, such a collagen fibers, which canbe sewn or draped upon a fissure or incision and then crosslinked to thetissue to provide closure. Once in place, the suture material isirradiated with laser or other high intensity light energy to fuse thesuture to the anastomotic site.

Alternatively, as shown in FIG. 3, the suture material 36 can include ahigh tensile strength core element 40 and an outer cross-linkable agent38 which are likewise used to sew or drape the anastomotic site prior toirradiation and fusion.

In another embodiment, as shown in FIG. 4, a suture material 36A can beemployed which is fabricated in a zig-zag strip form and applieddirectly upon the incision or fissure 32 to close the opening. Again,suture material 36A can include a high tensile strength core element 40and an outer cross-linkable agent 38.

In further embodiments 36B and 36C, shown in FIGS. 5 and 6,respectively, the suture material can be fabricated as a patch with ahigh strength element 40 incorporated into the structure, and alsoincluding a crosslinking agent 38 to join the suture material to theunderlying tissue and thereby effect closure of the anastomotic site 32.In the embodiments of FIGS. 5 and 6, the high strength element 40 can befabricated, for example, from the same material as the bonding agent 38,but pre-crosslinked to provide the addition resistance to tearing orshearing forces as the wound heals.

The present invention can employ various materials as crosslinkingagents in either solid, liquid, gel or powder form to form a bond totissue segments and thereby hold them together while natural healingprocesses occur. The crosslinking agents should be biocompatible and arepreferably biodegradable over time in vivo. Examples of suchcrosslinking agents include collagen, elastin, fibrin, albumin andvarious other photoreactive polymeric materials.

Various strength enhancing agents can also be incorporated into thesuture structure to provide additional tensile support along and acrossthe anastomosis. Such high tensile strength elements can be formed frompre-crosslinked segments of the same material that forms thephotoreactive crosslinking agent, or they can be formed from strips orfibers of other natural or synthetic biodegradable materials such aspolyesters, to enhance the strength of the bond.

In FIG. 7, a detachable carrier 37 is shown for use in applying azig-zag type strip of crosslinking agent 36 to an anastomotic site 32.In one preferred embodiment, the detachable carrier 37 is substantiallytransparent to photo-irradiation and can be detached from saidcrosslinking agent 36 following the bonding of the agent to thebiological material.

In FIG. 8, a tubular suture material 36 is shown for repairing a tornblood vessel 31 or other body tube or lumen. The suture material 36preferably includes a crosslinking agent 38 and reinforcing elementswhich can be braided, woven or simply matted fibers 40. In use, thesuture material is either fitted over the severed lumen (in the case ofa tube-shaped suture material) or wrapped around the severed biologicalstructure (e.g., with a strip-like suture material), and then irradiatedto crosslink the materials together. In some applications, the tubularsuture material 36 of FIG. 8 can be designed to shrink as thecrosslinking reaction occurs and thereby more tightly wrap theanastomotic site. In such procedures, it may also be preferable to firstdispose a stent 33 or similar support within the lumen to preventcollapse.

In FIG. 9, a staple structure 37 is shown incorporating a crosslinkingagent 36 on each prong such that the staple can be applied to close awound and then fused in place by application of laser radiation to thecrosslinking agent 36. Alternatively, the entire staple can be formedfrom a crosslinking agent and then irradiated (e.g., such that theexposed prongs are melted into tissue-bonding balls) to fuse the staplein place. (A similar approach can be taken to "knot," or otherwisesecure conventionally sewn sutures when a crosslinking agent comprises,or forms part of, the suture thread; in such an application, the surgeonwould put the stitches in place and then irradiate the site in order tobond the suture thread to tissue or itself and thereby increase thestrength of the closure.)

The present invention can be practiced with a wide variety of lasersources, including both gas and solid state lasers, operating in eithercontinuous wave ("c.w.") or pulsed modes. More specifically, the lasersources can be carbon monoxide, carbon dioxide, argon lasers or variousexcimer lasers utilizing mixtures of halogen and noble gases, such asargon-flouride, krypton-fluoride, xenon-chloride and xenon-fluoride.Additionally, the laser can be a solid state laser employing a rare,earth-doped Yttrium Aluminum Garnet (YAG) or Yttrium Lithium Fluoride(YLF) or a Yttrium-Scandium-Gadolinium-Garnet (YSGG) laser.

In one preferred embodiment, the laser source is a rare, earth-doped,solid state laser, such as a holmium-doped, erbium-doped orthulium-doped solid state laser of the YAG, YLF or YSGG type which canbe operated in a low wattage c.w. or pulsed mode with an outputwavelength in the range of about 1.4 to about 2.5 micrometers and apower density of about 0.1 watt/mm² to about 1.0 watt/mm². Such lasersources are disclosed in U.S. Pat. No. 4,917,084 issued on Apr. 17,1990, to the present inventor and incorporated herein by reference.

The absorption of laser energy from such solid state laser sources bybiological tissues is relatively high in relation to the absorption ofsuch energy by water, thereby providing an absorption length in thesubject's body of about 100 microns or more. Thus, it is possible tooperate satisfactorily even with 10-20 micrometers of blood between thehandpiece tip and the anastomotic site.

FIG. 10 is a schematic illustration of laser source 12, including asolid-state laser crystal 41, vacuum chamber 42 and diode pump source44. The laser crystal 41 is preferably surrounded by a cooling quartz orfused-silica jacket 46 having inlet pipe 48 and an outlet pipe 50 forcirculation of liquid nitrogen or other cryogenic coolant. The lasercavity can be formed by input crystal face coating 52 andpartially-reflective output mirror 54.

Generally, the laser crystal 41 is excited by optical pumping, thatbeing, irradiation of the crystal with light from the laser diode 44.(The diode 44 can be cooled by a pumped coolant or employ a heatsink).Both ends of the laser crystal 41 are preferably polished flat. Theinput face of the crystal 41 is preferably finished with a coating 52for high transmittance at the pump wavelength and high reflectance ofthe output wavelength. The other end of the crystal 41 preferablyincludes an antireflective coating 50 for high transmittal of the outputwavelength. The entire cavity of the reflector preferably is evacuatedto provide thermal insulation and avoid moisture condensation.

For further details on the construction of cryogenic, solid-statelasers, see, for example, an article by Barnes et al., Vol. 190, Societyof the Photo-Optical Instrumentation Engineers, pp. 297-304 (1979),NASA/JPL Technical Brief No. NPO-17282/6780 by Hemmati (June, 1988) andabove-referenced U.S. Pat. No. 4,917,084, all of which are hereinincorporated by reference.

Also shown in FIG. 10 is a tuning element 26 which can include, forexample, a birefringent crystal 28 disposed along the beam path 58 at aslight offset from Brewster's angle. The crystal 28 can be tunedelectro-optically by application of a voltage, as shown schematically inthe figure. Alternatively, the laser wavelength can be tunedmechanically by tilting or rotating the crystal 28 relative to the beampath using techniques well known in the art.

In FIG., 11 a partial, cross-sectional side view of a handpiece 64 isshown, including a casing 70 adapted for gripping by the clinical userand multiple lumens disposed therein. With further reference to FIG. 12as well, the handpiece serves to deliver laser irradiation suitable forbiological tissue fusion via a central optical fiber 72 connected tolaser source, as well as one or more additional illumination fibers 74for the delivery of illumination light and the transmittal of reflectedlight. The surgical laser delivery fiber 72 is preferable a low,hydroxyl ion content silica fiber. As shown in FIG. 12, the handpiece 64can deliver illumination light via fibers 74. In one embodiment, thesefibers 74 can also be used to collect reflective light and deliver it toa controller. Alternatively, some of the fibers 74 can be devotedentirely to collection of reflected light. The handpiece 64 can furtherinclude one or more lens elements 76, as well as a transparentprotective cover element or terminal lens 82.

FIG. 13 shows an apparatus 81 for remote application of suturesaccording to the invention. The apparatus 81 can be incorporated into acatheter, endoscope or arthroscope and disposed adjacent to a remoteanastomotic site. As shown, apparatus 81 includes a suture means 85 anda laser means 83. The suture port 85 delivers a photoreactive suturematerial to the anastomotic site, the suture material comprising astructure with at least a portion of the structure formed by acrosslinking agent such that upon irradiation of said suture means thecrosslinking agent adheres to the biological material and therebyprovides closure at said anastomotic site. The laser means 83 providesthe necessary light energy in the form of laser radiation to effectcrosslinking of the suture material at the anastomotic site. Theapparatus 81 can also include a viewing port 87, an illumination port 89and a reflectance sensing port 91 to provide a display and monitoring ofthe crosslinking process, as described in more detail below.

FIG. 14 is a more detailed schematic diagram of a reflectance monitor18, including a coupling port 90 for coupling with one or more fibers 76to receive reflectance signals from the handpiece of FIG. 4 or theapparatus of FIG. 13. The reflectance monitor 18 can further include afocusing lens 92 and first and second beam splitting elements 94 and 96,which serve to divide the reflected light into 3 (or more) differentbeams for processing.

As shown in FIG. 14, a first beam is transmitted to a first opticalfilter 98 to detector 102 (providing, for example, measurement ofreflected light at wavelengths shorter than 0.7 micrometers). A secondportion of the reflected light signal is transmitted by beam splitter 96through a second optical filter 100 to detector 104 (e.g., providingmeasurement of light at wavelengths shorter than 1.1 micrometers).Finally, a third portion of the reflected light is transmitted tophotodetector 106 (e.g., for measurement of reflected light atwavelengths greater than 1.6 micrometers). Each of the detector elements102, 104, and 106 generate electrical signals in response to theintensity of light at particular wavelengths.

The detector elements 102, 104 and 106 preferably include synchronousdemodulation circuitry and are used in conjunction with a modulatedillumination source to suppress any artifacts caused by stray light orthe ambient environment. (It should be apparent that other opticalarrangements can be employed to obtain multiple wavelength analysis,including the use, for example, of dichroic elements, either asbeamsplitters or in conjunction with such beamsplitters, to effectivelypass particular wavelengths to specific detector elements. It shouldalso be apparent that more than three discreet wavelengths can bemeasured, depending upon the particular application.) The signals fromthe detector elements can then be transmitted to a controller and/or adisplay element (as shown in FIG. 1).

In the controller, signals from the reflectance monitor are analyzed (asdetailed below) to determine the degree of crosslinking which isoccurring in the suture material and/or in the biological tissue exposedto the laser radiation. Such analysis can generate control signals whichwill progressively reduce the laser output energy over time as aparticular site experiences cumulative exposure. The control signals canfurther provide for an automatic shut-off of the laser when the optimalstate of crosslinking has been exceeded and/or the onset ofcarbonization is occurring.

As shown in FIG. 15, the data from the reflectance monitor can also beprovided directly to the clinician. In FIG. 15, a simulated view from aneyepiece 110 is shown in which the field of view 112 includes a fissureor cleavage line 114 dividing separate bodies at an anastomotic site.Also shown within the field of view is the suture material 36, a fusiontrack 116 which has been formed by laser radiation, and a presentexposure zone 118. Also displayed within the eyepiece 110 is a"heads-up" display of the reflectance values for the reflectance monitorof FIG. 14, including illuminated warning lights 122 which serve toindicate the reflectance intensity at particular wavelengths or otheroptical data indicative of the degree of crosslinking and/or tissuefusion.

In use, the apparatus of the present invention can be employed toanalyze the degree of crosslinking by comparing the reflectance ratiosof a site at two or more wavelengths. Preferably, intensity readings forthree or more wavelength ranges are employed in order to accuratelyassess the degree of crosslinking and to ensure that the optimal stateis not exceeded. The particular wavelengths to be monitored will, ofcourse, vary with the particular tissue undergoing treatment. Althoughthe tissue type, (e.g., blood-containing tissue or that which isrelatively blood-free) will vary, the general principles of theinvention, as disclosed herein, can be readily applied by those skilledin the art to diverse procedures in which the fusion of biologicalmaterials is desired.

For example, it is known that carbonization of many tissue types isaccompanied by a decrease in visible light reflectance and an increasein infrared reflectance. Thus, the analyzing circuitry of the controllercan be constructed to provide a warning (or automatically shut off thelaser radiation) when darkening in the visible wavelengths occurs orwhen the ratio of visible to infrared values falls below a predefinedlevel.

Moreover, when the material to be joined (e.g., aortic tissue) isrelatively unpigmented, reliance on changes in the reflectance ofvisible light can be inaccurate, but infrared reflectance changes (e.g.,above 1.1 micrometers) can reliably indicate the degree of crosslinking.(Lack of change in the visible reflectance is one of the reasons thattissues of this type are difficult to crosslink, as no change in thetarget's visible properties are observed until the tissue is overexposedto laser energy.) Consequently, the analyzing circuitry can monitorinfrared reflectance changes (e.g., greater than about 1.0 micrometers)as an indicator of proper crosslinking.

Finally, the reflectance sensor can also be used as a proximity monitorto ensue that the laser is in fact disposed at a proper distance fromthe anastomic site. By measuring total reflectance (over the entirevisible-infrared range or a portion thereof), a sudden drop in thereflectance value will typically be related to incorrect placement ofthe handpiece. Thus, the analyzing circuitry can sense the changes inreflectance and generate a warning to the user (or automatically shutoff the system) until proper placement is achieved.

What is claimed is:
 1. An apparatus for joining biological materialscomprising:a suture means for delivering a photoreactive suture materialto an anastomotic site, the suture material comprising a structure withat least a portion of the structure formed by a crosslinking agent suchthat upon irradiation of said suture means the crosslinking agentadheres to the biological material and thereby provides closure at saidanastomotic site; laser means for delivering laser radiation to saidanastomotic site to activate the crosslinking agent; and a surgicaltool, housing at least a portion of both said suture means and saidlaser means.
 2. Apparatus according to claim 1 wherein said suture meansfurther comprises a structure which is biodegradable over time in vivo.3. Apparatus according to claim 1 wherein the crosslinking agentcomprises at least one agent chosen from the group consisting ofcollagen, elastin, fibrin and albumin.
 4. Apparatus according to claim 1wherein the structure further comprises a crosslinking agent and atleast one high tensile strength element which inhibits tears in saidstructure.
 5. Apparatus according to claim 1 wherein the high tensilestrength element is connected to said cross-linking agent, such that,upon irradiation, the high strength element and biological material arejoined to each other to enhance bond strength.
 6. Apparatus according toclaim 1 wherein the structure is adapted to placed around a tubularbiological structure for repair purposes.
 7. Apparatus according toclaim 1 wherein the laser means further comprises a laser generating anoutput wavelength ranging from about 1.4 to about 2.5 micrometers. 8.Apparatus according to claim 1 wherein the apparatus further includesanalyzing means for determining the degree of crosslinking within anexposure zone based on said plurality of reflectance intensitymeasurements at distinct wavelengths.